In addition to the rapid spread of wireless LAN equipment represented by IEEE 802.11b, by wirelessly interconnecting AV equipment or personal computers, a seamless network is expected to be established in the society. Under such circumstances, establishment of technologies for realizing small size and high-speed data transmitting apparatuses, receiving apparatuses and communication systems at a low cost has been urgently required.
As one of such technologies, much attention has been focused on a communication method called Ultra Wide Band (hereinafter, referred to as “UWB”) using a pulse modulation signal.
As a conventional transmitting apparatus used in pulse wireless communication, for example, a configuration described in Japanese Translation of PCT Publication No. 2003-513501 is known. FIG. 26 shows a conventional pulse generation circuit described in Japanese Translation of PCT Publication No. 2003-513501.
A pulse generating circuit shown in FIG. 26 includes analog waveform generating circuit 5801 for generating an arbitrary analog waveform signal, inductor 5802 and circuit 5803 including a negative resistance element having a stable region and an unstable region. Circuit 5803 including a negative resistance element changes its operation state into a stable region and an unstable region in response to the analog waveform signal and oscillates in the unstable region. Thereby, one pulse of the analog waveform signal is split into a plurality of short pulses so as to obtain a wavelet signal as a modulation signal. A wavelet is a momentarily existing AC wave.
FIG. 27 is a block diagram showing a configuration of a conventional transmitting apparatus. This conventional transmitting apparatus 6213 includes first to fourth pulse generators 6203 to 6206. Pulses generated by pulse generators 6203 to 6206 based on signals from pulse source 6201 and highest order unit 6202 are orthogonal to each other. As the pulses that are orthogonal to each other, modified Hermite orthogonal pulses are used. Pulse selector/synthesizer 6207 selects and synthesizes orthogonal pulses based on data input. A multiplexed signal is amplified by amplifier 6209 in transmitting unit 6208 and transmitted via antenna 6210. A conventional receiving apparatus (not shown) uses the orthogonality of the pulses and separates them, thereby separating and demodulating the multiplexed signal. The above-mentioned configuration is disclosed in, for example, Japanese Patent Unexamined Publication No. 2003-87220.
FIG. 28 shows a modulation waveform of a conventional transmitting apparatus that is different from that of FIG. 27. In the conventional example shown in FIG. 27, by allowing pulses to be orthogonal to each other, the information amount per unit time is increased. In this conventional example, by giving information to both a pulse position and a phase thereof, the information amount is increased. In FIG. 28, “information (BIP)” represents a content providing Bi-Phase modulation, “information (PPM)” represents a content providing pulse position modulation, and “diffusion” represents a content providing diffusion processing, respectively. A “waveform” shows a waveform provided with them. The above-mentioned conventional configuration is disclosed in, for example, Japanese Patent Unexamined Publication No. 2003-101509.
However, in the conventional configuration described in Japanese Translation of PCT Publication No. 2003-513501, since information is conveyed by PWM (Pulse Width Modulation), which converts an analog waveform signal into a wavelet corresponding to the duration of the analog waveform signal, the increase in the amount of information to be transmitted leads to the increase of the width of the wavelet, which may make it difficult to increase the density of the amount of information to be conveyed.
In the conventional configuration described in Japanese Patent Unexamined Publication No. 2003-87220, since the transmitting apparatus requires complex pulse waveform generation, it may be difficult to generate a desired waveform in a very short wavelet having a wavelet width of less than 1 ns. In order to achieve a very short wavelet, a complex circuit configuration is required. Thus, the cost rises and power consumption may be increased. Meanwhile, in the conventional configuration described in Japanese Patent Unexamined Publication No. 2003-101509, when the interval of wavelets is made extremely narrow with respect to the width of the wavelet, it may be difficult to separate the wavelets in the receiving apparatus, the transmitting apparatus cannot allow the intervals of wavelets to be extremely narrow. Thus, it may be difficult to improve the communication speed.